1. Field of the Invention
The present invention pertains generally to air-cooled internal combustion engines, and more particularly to a cast cylinder assembly for such an engine having an intake cross-passageway cast integrally therewith.
2. Description of Related Art
A known configuration of an air-cooled single cylinder internal combustion engine involves an arrangement wherein the crankshaft is disposed vertically and the cylinder and piston bore are horizontal. The intake and exhaust valves are located side-by-side relatively close to one another on one side of the cylinder with the intake valve located above the exhaust valve. The valves are oriented parallel to the piston bore and the valve heads and valve seats are located near the head of the cylinder at the interface between the cylinder and the cylinder head. A valve cavity associated with each of the intake and exhaust valves communicates with the piston bore around the respective valve head (when the valve is open) via a connecting passageway in the cylinder head. The valves are lifted and opened in appropriate sequence by a common camshaft located in the crankcase.
It is desireable that the carburetor and muffler be located on opposite sides of the cylinder to avoid the deleterious effects of exhaust heat on the operation of the carburetor and to avoid the safety hazard caused by proximity of the muffler to the fuel in the carburetor. The disposition of the intake and exhaust valves immediately next to one another on the same side of the cylinder is in conflict with the desired arrangement of the carburetor and muffler. Consequently, it is known to route an external intake tube from the intake valve cavity over across the cylinder to the carburetor located on the opposite side. This arrangement adds to the cost of the engine by requiring the manufacture and connection of a separate component, namely the external tube. Furthermore, by having the intake valve located above the exhaust valve and by routing the intake tube over the cylinder, the carburetor must be mounted relatively high with respect to the mounting base of the engine. This reduces the space available above the carburetor for mounting a gravity feed fuel tank, so that the volume of the tank must be sacrificed or else the overall profile of the engine must suffer an increase in height. Also, the disposition of the exhaust valve below the intake valve results in less efficient cooling of the exhaust valve because it is less exposed to the flow of cooling air.
A known arrangement of a partially cast intake tube crossing over the cylinder is shown in U.S. Pat. No. 4,548,167. The cylinder assembly shown therein provides an intake passageway which is for the most part cast integrally with the cylinder. An opening in the side of the passageway is provided in view of casting considerations to allow removal of the casting core. The opening is closed by a separate cover bolted to the cylinder. The interface between the cover and cylinder is a peripheral planar surface which intersects the passageway at the opening at an acute angle, with the cover being disposed exteriorly of the opening. A manufacturing disadvantage of the arrangement of U.S. Pat. No. 4,548,167 is that after casting, flashing can be present around the peripheral planar sealing surface and can extend into the passageway.
It would be desireable to provide a cast cylinder assembly for a horizontal cylinder air-cooled engine in which an intake cross-passageway connecting the intake valve on one side of the cylinder with the carburetor on the other side of the cylinder is provided at lower manufacturing cost. The present invention accomplishes this goal.